A one-way analysis of variance and thermal analysis were performed in this review to examine the influences of the contents, types, and forms of chemical foaming brokers, in addition to the usage of coupling agents, on the density reduction and cell morphology of extrusion-foamed neat high density polyethylene and HDPE/wood-flour composites. The CFA forms and types did not affect the void fractions of both neat HDPE and double screw extruder HDPE/wood-flour composites. However, a gas containment limit was noticed for neat HDPE foams whereas the average cell size accomplished in the HDPE/wood-flour composite foams remained insensitive to the CFA contents, regardless of the foaming agent types. The experimental outcomes indicated that the use of coupling agent in the formulation was required to accomplish HDPE/wood-flour composite foams with high void fraction.